Accompanying the trend toward high-frequency band of signals applied to the multi-layered ceramic wiring board in recent years, it is required to use a material selected from low-resistance metals such as copper and silver as a conductor forming a wiring layer, which must transfer signals without loss in the high-frequency regions. In the use of such low-resistance metals as conductive materials, a substrate material must be able to be baked at a low temperature of 1,000° C. or less. A ceramic composition containing a diopside crystal as a primary crystal is one of known examples of substrate materials having such characteristics.
As a ceramic composition utilizing a diopside crystal, a Japanese Patent Publication JP 2000-128628 discloses a glass ceramic composition made from 50 to 100% of crystalline glass powder and 0 to 50% of filler powder in mass percentages, in which the crystalline glass powder has a composition consisting of 40 to 65% of SiO2, 10 to 20% (exclusive of 20%) of CaO, 11 to 30% of MgO, 0.5 to 10% of Al2O3, 0.01 to 1% of CuO, 0 to 25% of SrO, 0 to 25% of BaO, and 0 to 25% of ZnO, wherein a diopside is deposited as a primary crystal in a crystal form and/or a solid solution crystal form. It is described in the publication that, with the glass ceramic composition, the metal Ag co-fired to form an inner conductor is not diffused in the glass ceramic. In addition, the publication described that a multi-layered board having small dielectric loss can be made of the glass ceramic composition, being well adaptive to the electronic circuits to which the high-frequency band of signals is applied.
Further, a Japanese Patent Publication JP 2001-278657 discloses a porcelain composition baked at a low temperature containing a diopside crystal (CaMgSi2O6) as a primary crystal, being characterized with a dielectric constant ∈ of 7 or less and a Q×f value of 10,000 GHz or more. It is described in the publication that, with the porcelain composition, a wiring board that can be baked at a temperature of 1,000° C. or less and has excellent dielectric characteristics in the high frequency regions can be obtained.
However, in the case of the technology as disclosed in JP 2000-128628, there arise problems in a fact that crystalline glass powder used as a raw material elevates the cost and a fact that it is not easy to handle. Further, a relatively high CaO content results in formation of forsterite crystal as a side product, which tends to cause a reduction in strength.
Further, in the technology as disclosed in JP 2001-278657, formation of side products such as wollastonite crystal and forsterite crystal tends to cause a reduction in strength. Furthermore, when a ceramic layer is utilized for the electronic component region forming a capacitor, a filter and the like, the higher dielectric constant copes with downsizing. In this case, however, the dielectric constant is 7 or less, so that it is difficult to obtain the one having a small size with good properties. Thus, it has been difficult to meet the requirement of high integration.